Project import generated by Copybara.

GitOrigin-RevId: 19a829ffd755edb43e54d20c0e7b9348512d5108

mediapipe/framework/graph_service.h

@@ -16,6 +16,12 @@
 #define MEDIAPIPE_FRAMEWORK_GRAPH_SERVICE_H_
 
 #include <memory>
+#include <type_traits>
+#include <utility>
+
+#include "absl/strings/str_cat.h"
+#include "mediapipe/framework/packet.h"
+#include "mediapipe/framework/port/status.h"
 
 namespace mediapipe {
 
@@ -27,18 +33,74 @@ namespace mediapipe {
 // IMPORTANT: this is an experimental API. Get in touch with the MediaPipe team
 // if you want to use it. In most cases, you should use a side packet instead.
 
-struct GraphServiceBase {
+class GraphServiceBase {
+ public:
+  // TODO: fix services for which default init is broken, remove
+  // this setting.
+  enum DefaultInitSupport {
+    kAllowDefaultInitialization,
+    kDisallowDefaultInitialization
+  };
+
   constexpr GraphServiceBase(const char* key) : key(key) {}
 
+  virtual ~GraphServiceBase() = default;
+  inline virtual absl::StatusOr<Packet> CreateDefaultObject() const {
+    return DefaultInitializationUnsupported();
+  }
+
   const char* key;
+
+ protected:
+  absl::Status DefaultInitializationUnsupported() const {
+    return absl::UnimplementedError(absl::StrCat(
+        "Graph service '", key, "' does not support default initialization"));
+  }
 };
 
 template <typename T>
-struct GraphService : public GraphServiceBase {
+class GraphService : public GraphServiceBase {
+ public:
   using type = T;
   using packet_type = std::shared_ptr<T>;
 
-  constexpr GraphService(const char* key) : GraphServiceBase(key) {}
+  constexpr GraphService(const char* my_key, DefaultInitSupport default_init =
+                                                 kDisallowDefaultInitialization)
+      : GraphServiceBase(my_key), default_init_(default_init) {}
+
+  absl::StatusOr<Packet> CreateDefaultObject() const override {
+    if (default_init_ != kAllowDefaultInitialization) {
+      return DefaultInitializationUnsupported();
+    }
+    auto packet_or = CreateDefaultObjectInternal();
+    if (packet_or.ok()) {
+      return MakePacket<std::shared_ptr<T>>(std::move(packet_or).value());
+    } else {
+      return packet_or.status();
+    }
+  }
+
+ private:
+  absl::StatusOr<std::shared_ptr<T>> CreateDefaultObjectInternal() const {
+    auto call_create = [](auto x) -> decltype(decltype(x)::type::Create()) {
+      return decltype(x)::type::Create();
+    };
+    if constexpr (std::is_invocable_r_v<absl::StatusOr<std::shared_ptr<T>>,
+                                        decltype(call_create), type_tag<T>>) {
+      return T::Create();
+    }
+    if constexpr (std::is_default_constructible_v<T>) {
+      return std::make_shared<T>();
+    }
+    return DefaultInitializationUnsupported();
+  }
+
+  template <class U>
+  struct type_tag {
+    using type = U;
+  };
+
+  DefaultInitSupport default_init_;
 };
 
 template <typename T>